1. Field of the Invention
The present invention relates generally to improvements to techniques used to splice optical fiber, and more particularly to advantageous aspects of systems and methods for fabricating low-loss, high-strength optical fiber transmission lines.
2. Description of the Prior Art
A new class of optical fibers has recently been developed known as inverse dispersion fibers (IDFs), including dispersion-compensating fibers (DCFs), which have a steeply sloped, negative dispersion characteristic. One use for DCF is to optimize the dispersion characteristics of already existing optical fiber links fabricated from standard single-mode fibers (SSMF) for operation at a different wavelength. This technique is disclosed in U.S. patent application Ser. No. 09/596,454, filed on Jun. 19, 2000, assigned to the assignee of the present application, which is hereby incorporated by reference in its entirety.
An important parameter for DCF is the excess loss that results when an optical fiber transmission line is fabricated by splicing DCF to other types of fiber, such as SSMF. To obtain a highly negative dispersion, DCF uses a small core with a high refractive index, having a modefield diameter of approximately 5.0 μm at 1550 nm, compared with the approximately 10.5 μm modefield diameter of SSMF at 1550 nm. The difference in core diameters results in significant signal loss when a fusion splicing technique is used to connect DCF to SSMF. It is possible to reduce the amount of signal loss by choosing splicing parameters that allow the core of the DCF to diffuse, thereby causing the modefield diameter of the DCF core to taper outwards, resulting in a funneling effect. However, the high concentration of fluorine dopant in typical DCF limits the application of this technique, because the amount and duration of the heat required to produce the funneling effect may result in an undesirable scattered diffusion of the fluorine dopant.
Further, in certain applications, such as in submarine systems, splice strengths of 200 kpsi or more are required. Accordingly, there is a need for improved systems and method for fabricating low-loss, high-strength optical fiber transmission lines.